Correlating angiograms with CT/MRI scans for radiosurgery.

A mathematical solution is described to reconstruct 3-D objects in the stereotactic space from angiographic, not necessarily perpendicular 2-D projections. The mathematical calculation requires 6 markers, whose coordinates should be known within the stereotactic frame reference system. This method was developed to improve the planning in stereotactic radiosurgery of AVM. An AVM nidus can be geometrically described as delineated on plane film angiography. This approach provides a more accurate determination of the lesion shape, size, angulation and position when using information from stereotactic planar angiograms. Further more this technique supports a stereotactically accurate projection of the surface volume model of the AVM nidus on to the corresponding CT and MRI scans images.

An afterloading 192Ir surface mold.

Patients with basal cell skin cancer can be treated with afterloading 192Ir surface molds constructed from dental wax. High activity 192Ir seeds in ribbons are distributed in the mold to uniformly irradiate the target volume. The treatment is preplanned with a treatment planning system to achieve a uniform dose distribution in the planned target volume. The implant parameters optimized include the seed strength and number of seeds, inter- and intracatheter spacing between 192Ir seeds, and the distance between the implant and treatment planes. The radioactive 192Ir strands are afterloaded in the catheters embedded in the wax mold and the position secured with buttons. The treatment area drawn on the patient surface is visually overlapped with the uniformly irradiated area sketched on the mold surface. The mold is taped to the head to secure this position. The dose rate on the surface of the mold in contact with the patient skin is measured with calibrated LiF TLD chips and is within +/- 5% of the computer preplanned dose rate value. This technique is a viable alternative to external beam treatments when daily treatments are not feasible and a dose distribution conforming to the treatment area is desirable.

Carcinogenic effects of scattered dose associated with radiation therapy.

Ionizing radiation has long been recognized as a weak carcinogen, and the risk of developing a radiation induced neoplasm after exposure to therapeutic radiation has been established. In the case of therapeutic radiation for treatment of existing malignancies, concomitant risk factors for second malignancies can confound the effect of radiation alone. This study presents a model for evaluating the isolated contribution of ionizing radiation to the induction of second malignancies in cancer patients, and presents estimates of the expected number of second malignancies induced in selected sensitive sites by scatter radiation during radiotherapy for cancer. The study focused on the year 1987, during which it was estimated that 192,761 new cancer patients received radiotherapy as part of their initial treatment plan. The model predicted that radiation may induce 63-84 secondary breast cancers, 64-72 secondary thyroid cancers, 94-157 secondary lung cancers, and 489-707 secondary leukemias over the remaining lifetime of this patient population. This represents a lifetime incidence of 0.7% for leukemia, and 0.3% for the solid tumors. This incidence must be placed in perspective with the current concepts of cancer management, such as combined modality therapy that may carry a risk of carcinogenesis greater than either modality alone, and when the alternatives to radiotherapy may be nonexistent or may be cosmetically or functionally undesirable. The information presented may be used in weighing the risks and benefits of alternative treatments for cancer.

Digital image processing of radiation therapy portal films.

Digital image processing has the potential to enhance and improve several functions of a modern radiation oncology department. These functions may include improving perception of information for low contrast films, electronic transfer of images to remote facilities and back, and reducing storage space requirements for archiving once treatment is finished. This paper gives an overview of the digitization process and of image processing fundamentals. The clinical evaluation of digitized portal films is also discussed. The authors conclude that digitizing low contrast radiation therapy portal films is feasible with present technology and will produce images acceptable for routine clinical use in most instances. The role of image enhancement is less well established and remains investigational.

Medulloblastoma: treatment results and effect on normal tissues.

Thirty-three children under age 20 with medulloblastoma, treated between 1962 and 1976, at the University of California and the Claire Zellerback Saroni Tumor Institute of Mount Zion Hospital, San Francisco, were retrospectively studied. A relationship between dose and local control rate was suggested by an improved five-year survival in those patients receiving doses greater than 5000 rads to the posterior fossa. The posterior fossa, either alone or with the spinal cord, was the most frequent site of failure. Results of re-irradiation for failure were encouraging and no significant complications were noted. A study of the effects of craniospinal irradiation on the hematopoietic and immune system demonstrated a marked decrease in the peripheral lymphocyte population at the completion of therapy and suggested a functional impairment of the remaining lymphocytes. Other side effects of irradiation included suppression of the hypothalamic-pituitary axis and one instance of brain necrosis. Current treatment policy and proposals for future modifications are discussed.